I'm thinking that is only his ceremonial armor. Looking at the helmet, you see it is very open in the front, not ideal for combat. But his helmet in the picture above, from Halo: Escalation, that's a combat helmet.It's sealed up in the front, and looks intimidating. I think he'll do politics and combat in Halo 5. He won't be reduced to just a narrator. He may not be playable but Thel 'Vadam won't be sitting around when there is work to be done.